A fungus known to infect and kill gypsy moth caterpillars may help lower the insects' population in West Michigan in the next couple years, according to Rebecca Finneran, a horticultural expert with the Michigan State University Extension program in Grand Rapids.(Ben Allan Smith | MLive.com)

A population surge brought about by a pair of dry spring seasons in 2016 and 2017 has made gypsy moths a hot button issue over the past year for residents in numerous West Michigan communities.

On top of cropping up in their usual haunts in places like Wyoming and Cascade Township, as well as other areas, the insects have also managed to make appearances in communities such as Gaines, Caledonia and Ada townships -- areas where the gypsy moth has not been too troublesome in recent years.

Known to defoliate a wide variety of trees, oak foremost among them, and to make a mess of homeowners' properties in general, communities sometimes resort to spraying a bacterial agent called Bacillus thuringiensis, or B.t., to suppress gypsy moth populations.

While Wyoming, Walker, Kentwood and Cascade Township have been spraying for consecutive years, and other communities, such as Gaines and Caledonia townships, are considering employing the bacterial agent as well, a horticulture expert with the Michigan State University Extension program says nature may well take care of the problem itself in the next couple years.

Rebecca Finneran, a horticultural educator with the MSU Extension in Grand Rapids for over three decades, said conditions were wet enough this spring that a natural pathogen known as Entomophaga maimaiga, a fungus that infects and kills gypsy moth caterpillars, will most likely decrease West Michigan's gypsy moth population in the coming year.

"Entomophaga infects caterpillars, causing a disease that kills them," Finneran wrote in an article published on the MSU Extension website in late June. "A source of the next season's fungal spores, the dead caterpillar, which can hold thousands of spores that will infect gypsy moth caterpillars next spring, ends up being the best bet for control."

Finneran said when weather patterns are dry, as they were during those two consecutive spring seasons in 2016 and 2017, the fungus is not able to reproduce enough to infect the following season's caterpillars.

Though West Michigan experienced some odd weather patterns this spring, as well, such as the ice storm that hit the region in late April, Finneran said there was ample moisture to fuel the fungus' development this time around.

"Since May, some have noticed small, dried up caterpillars that did not develop fully because they were infected," she wrote. "Each one of these becomes filled with fungus and produces over 400,000 spores. These spores infect other caterpillars, which end up dying on the trunk of the tree, oddly enough always facing downward.

"These will eventually fall to the ground around the base of the tree, releasing thousands of resting spores that will infect the tiny caterpillars next spring."

Finneran said she is aware that many communities, after receiving complaints from residents, have been looking at potentially spraying for gypsy moths. While that approach may still be useful in some areas that are hit particularly hard, she said spraying on a large scale is probably not warranted.

"With high levels of Entomophaga-infected caterpillars seen this season, it is not likely to be as big a problem next year and even better the year after that," she said.